Phosphinidine-Palladium Complexes for the ... - ACS Publications

Received August 2, 2002. Several ... the pioneering studies of Wilke,2a Keim,2b and Klabunde ... Keim, W.; Kowaldt, F. H.; Goddard, R.; Krü ger, C. A...
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Organometallics 2002, 21, 5935-5943

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Phosphinidine-Palladium Complexes for the Polymerization and Oligomerization of Ethylene Olafs Daugulis, Maurice Brookhart,* and Peter S. White Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290 Received August 2, 2002

Several cationic palladium complexes containing bulky phosphinidine-imine, phosphinidine-sulfide, and imine-sulfide ligands have been prepared. These complexes catalyze the oligomerization and polymerization of ethylene with moderate to high rates (for palladium catalysts) and display higher stability compared to diimine-palladium systems. Introduction The development of well-defined late-transition metal catalysts for the polymerization of ethylene and R-olefins has been the subject of intense recent study.1 Following the pioneering studies of Wilke,2a Keim,2b and Klabunde and Ittel2c we disclosed highly versatile Ni(II) and Pd(II)-R-diimine-based catalysts of type 1.3a Hindered aryl groups on the R-diimine nitrogens block the axial coordination sites and retard chain transfer relative to propagation, resulting in high molecular weight polymer. These complexes polymerize ethylene, producing polyethylene with microstructures ranging from almost linear to hyperbranched depending on the catalyst used and reaction variables.3b,c Nickel catalysts are stable for hours at room temperature;3d however, in the case of palladium catalysts, lowering of reaction temperature to 5 °C is necessary to achieve living polymerization and prevent substantial catalyst decomposition.3e Recently, cationic palladium-diphosphinidenecyclobutene complexes of type 2 were described by Ozawa, Yoshifuji, and co-workers.4 At 60-100 °C they catalyze the conversion of ethylene to polyethylene with moderate Mw’s (4000-33 000), high polydispersities (4.214.8), and moderate activities (up to 4500 TO/h at 70 °C). Noteworthy is the exceptional thermal stability of these complexes. Palladium-diimine catalysts deactivate at moderate rates at RT,3e and at 70 °C deactivation is observed within 15 min.4 Since arylphosphinidines and arylimines possess similar structural features, we sought to incorporate the phosphinidine functionality into one (1) For recent reviews see: (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169. (b) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428. (c) Mecking, S. Coord. Chem. Rev. 2000, 203, 325. (2) (a) Wilke, G. Angew. Chem., Int. Ed. Engl. 1988, 27, 185. (b) Keim, W.; Kowaldt, F. H.; Goddard, R.; Kru¨ger, C. Angew. Chem., Int. Ed. Engl. 1978, 17, 466. (c) Klabunde, U.; Ittel, S. D. J. Mol. Catal. 1987, 41, 123. (3) (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995, 117, 6414. (b) Brookhart, M. S.; Johnson, L. K.; Killian, C. M.; Arthur, S. D.; Feldman, J.; McCord, E. F.; McLain, S. J.; Kreutzer, K. A.; Bennett, M. A.; Coughlin, E. B.; Ittel, S. D.; Parthasarathy, A.; Tempel, D. J. WO 9623010, 1996. (c) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J. Science 1999, 283, 2059. (d) Gates, D. P.; Svejda, S. A.; On˜ate, E.; Killian, C. M.; Johnson, L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320. (e) Gottfried, A. C.; Brookhart, M. Macromolecules 2001, 34, 1140. (4) Ikeda, S.; Ohhata, F.; Miyoshi, M.; Tanaka, R.; Minami, T.; Ozawa, F.; Yoshifuji, M. Angew. Chem., Int. Ed. 2000, 39, 4512.

arm of bidentate Pd(II) complexes in the hope of imparting greater thermal stability to these catalysts. We report here synthesis and ethylene polymerization activity of a number of cationic phosphinidine-imine, phosphinidine-sulfide, and imine-sulfide palladium complexes. Results and Discussion 1. Pd(II) Catalysts Incorporating Phosphinidine-Imine Ligands. The most straightforward modification of the diimine system was the incorporation of both a phosphinidine and imine moiety into the catalysts. Starting phosphinidine-imine ligands were prepared taking advantage of elimination methodology developed by Bickelhaupt et al. for unstabilized phosphinidines.5 Imines 3a,b were deprotonated with LDA, followed by reaction with Mes*PCl2 (Mes* ) 2,4,6-tritert-butylphenyl). Elimination of HCl from the intermediate chlorophosphines using DBU afforded the requisite phosphinidine-imine ligands 4a,b as yellowred crystalline solids. In the case of more hindered 4a it was necessary to use acetonitrile as solvent and elevated temperatures in the elimination step to obtain a reasonable conversion to the phosphinidine (Scheme 1). (5) (a) Klebach, Th. C.; Lourens, R.; Bickelhaupt, F. J. Am. Chem. Soc. 1978, 100, 4886. (b) van der Knaap, Th. A.; Klebach, Th. C.; Visser, F.; Bickelhaupt, F.; Ros, P.; Baerends, E. J.; Stam, C. H.; Konijn, M. Tetrahedron 1984, 40, 765.

10.1021/om020631x CCC: $22.00 © 2002 American Chemical Society Publication on Web 11/23/2002

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Figure 1. ORTEP view of 4a. Selected interatomic distances (Å) and angles (deg): P(1)-C(2) ) 1.684(2), P(1)C(24) ) 1.85(2), N(5)-C(4) ) 1.288(3), C(4)-C(2) ) 1.484(3); C(24)-P(1)-C(2) ) 104.36(9), P(1)-C(2)-C(4) ) 116.36(15), C(2)-C(4)-N(5) ) 116.75(18). Scheme 1

Scheme 2

An X-ray structure of the ligand 4a was obtained to verify the geometry around the CdP and CdN bonds (Figure 1). As expected, a trans configuration of the imine and phosphinidine double bonds was observed. Bond lengths observed in 4a are common for phosphaalkenes6 (C(2)dP(1), 1.684(2) Å; C(24)-P(1), 1.850(2) Å). The C(24)-P(1)-C(2) angle of 104.36(9)° and C(24)-P(1)-C(2)-C(4) dihedral angle of -176.1(3)° are also typical for phosphinidines not bearing two bulky substituents on the carbon terminus of the PdC bond.6a Ligands 4a,b readily displace cod from (cod)PdMeCl7 to give single isomers of the corresponding complexes 5a,b in good yields. Chloride ion abstraction was effected by reaction of 5a,b with NaB(ArF)4 (ArF ) [3,5(CF3)2C6H3]) in acetonitrile/dichloromethane, affording cationic acetonitrile complexes 6a,b as yellow-red powders (Scheme 2). The phosphorus chemical shifts of the complexes 5a,b and 6a,b show considerable shielding (6) (a) Appel, R.; Menzel, J.; Knoch, F.; Volz, P. Z. Anorg. Allg. Chem. 1986, 534, 100. (b) van der Sluis, M.; Beverwijk, V.; Termaten, A.; Gavrilova, E.; Bickelhaupt, F.; Kooijman, H.; Veldman, N.; Spek, A. L. Organometallics 1997, 16, 1144. (c) Ma¨rkl, G.; Kreitmeier, P.; No¨th, H.; Polborn, K. Angew. Chem., Int. Ed. Engl. 1990, 29, 927. (d) Yoshifuji, M.; Toyota, K.; Murayama, M.; Yoshimura, H.; Okamoto, A.; Hirotsu, K.; Nagase, S. Chem. Lett. 1990, 2195. (e) van der Sluis, M.; Bickelhaupt, F.; Veldman, N.; Kooijman, H.; Spek, A. L.; Eisfeld, W.; Regitz, M. Chem. Ber. 1995, 128, 465. (f) Ito, S.; Toyota, K.; Yoshifuji, M. Chem. Lett. 1995, 747. (g) Appel, R.; Winkhaus, V.; Knoch, F. Chem. Ber. 1987, 120, 243. (7) Ru¨lke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; van Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.

Daugulis et al.

compared to the free ligands (δP, ppm: 4a, +303.0 ppm; 5a, +268.3; 6a, +267.4 ppm). The magnitude of Me-P coupling constants suggests that phosphorus is cis to the methyl group (6b, J Me-P, 1H; 2.6 Hz; 13C, 2.7 Hz; similar values for 5a,b and 6a).6b A single-crystal X-ray analysis confirmed the structure of 6a and its geometrical similarity to the corresponding diimine-palladium complexes. The crystal structure shows a square planar arrangement of the ligands around the palladium center. As expected from the spectral data, the methyl group on palladium is positioned cis to the phosphorus atom, suggesting a stronger trans-influence8 of the phosphinidine moiety. The P(1)dC(6) bond length in 6a is slightly shortened compared to free ligand 4a (1.660(11) vs 1.684(2) Å) and is comparable to the bond lengths in other phosphinidine-palladium complexes.9,10 The Pd-P bond length of 2.183(3) Å is shorter than in palladium-diphosphinidenecyclobutane complexes9a,b,d (2.23-2.33 Å) but similar to Pd-P lengths in palladium complexes of phosphinidine-pyridines6b and orthopalladated phosphinidines.10 The length of the N(14)dC(7) bond (1.287(15) Å) is in the standard range for palladium-imine complexes.11 The five-membered chelate ring is planar within two degrees. N-Aryl and P-aryl groups lie almost perpendicular to the plane of the five-membered ring (torsion angles: C(6)-P(1)-C(15)-C(20), 88.0(11)°, C(7)N(14)-C(33)-C(38), 96.5(15)°), efficiently blocking the axial coordination sites (Figure 2). Complexes 6a,b proved to be ethylene oligomerization catalysts and were studied at 26 °C and 400 psi ethylene. Results are summarized in Table 1. A turnover rate of 23 TO/h was observed for more hindered catalyst 6a in a 3 h run. Decreased hindrance in 6b gave rise to higher turnover numbers (94 TO/h) with a concurrent drop of oligomer molecular weight from 670 to 300. The catalysts are more stable than diimine-Pd complexes at RT; comparing entries 1 and 2 shows that 6a does not significantly deactivate in a 15 h run. In an effort to better understand this system, ethylene insertion barriers were measured for the less hindered mesitylimine system 6b. Cationic ethylene complex 7 was generated at -78 °C via the reaction of 5b with NaB(ArF)4 under excess olefin (20 equiv). Upon warming to -23 °C, migratory insertion of ethylene into the PdMe bond was observed with k ) 7.9 × 10-5 s-1, corresponding to ∆Gq ) 19.2(1) kcal/mol. After the disappearance of the Pd-Me signal, insertion of ethylene into Pd-alkyl bonds was measured giving k ) 2.4 × 10-4, ∆Gq ) 18.7(1) kcal/mol. For comparison, typical migratory insertion barriers in (diimine)palladium (methyl)(ethylene) complexes are ca. 17 kcal/mol.3a Since ∆∆Gq ) 2 kcal corresponds to k2/k1 ) 30 (25 °C), (8) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev. 1973, 10, 335. (9) (a) Minami, T.; Okamoto, H.; Ikeda, S.; Tanaka, R.; Ozawa, F.; Yoshifuji, M. Angew. Chem., Int. Ed. 2001, 40, 4501. (b) Toyota, K.; Masaki, K.; Abe, T.; Yoshifuji, M. Chem. Lett. 1995, 221. (c) Chentit, M.; Geoffroy, M.; Bernardinelli, G. Acta Crystallogr., Sect. C 1997, C53, 866. (d) Yamada, N.; Abe, K.; Toyota, K.; Yoshifuji, M. Org. Lett. 2002, 4, 569. (e) Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Chem. Commun. 1996, 437. (10) Kawanami, H.; Toyota, K.; Yoshifuji, M. Chem. Lett. 1996, 533. (11) (a) van Asselt, R.; Elsevier, C. J.; Smeets, W. J. J.; Spek, A. L.; Benedix, R. Recl. Trav. Chim. Pays-Bas 1994, 113, 88. (b) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.; Brookhart, M. J. Am. Chem. Soc. 2000, 122, 6686.

Phosphinidine-Palladium Complexes

Organometallics, Vol. 21, No. 26, 2002 5937 Table 2. Oligomerization/Polymerization of Ethylene by 11a and 14 at 26 °C, 400 psi in CH2Cl2 entry catalysta time, h g polymer TOF, h-1 1 2 3 4

11a 11a 14 14

3 15 3 8

3.6 12.5 2.6 5.2

4300 3000 3100 2300

Mnb

branchingc

215d

60 40 119 119

180d 2300 2500e

a 0.01 mmol of catalyst in 100 mL of CH Cl b 2 2 used. Mn determined by 1H NMR spectroscopy (see Experimental Section for details). c Branching determined by 1H NMR spectroscopy (see Experimental Section for details). d Butene, hexene, and octene fraction partially lost during evaporation of solvent (GC analysis). e GPC data: M ) 1900, M ) 2900, PDI ) 1.5. n w

Figure 2. ORTEP view of 6a. Selected interatomic distances (Å) and angles (deg): P(1)-Pd(1) ) 2.183(3), N(14)Pd(1) ) 2.166(8), Pd(1)-C(1) ) 2.052(10), Pd(1)-N(2) ) 2.063(10), P(1)-C(6) ) 1.660(11), P(1)-C(15) ) 1.799(9), N(14)-C(7) ) 1.287(15), N(2)-C(3) ) 1.107(17); C(6)P(1)-C(15) ) 113.7(5), C(7)-N(14)-C(33) ) 122.3(8). Table 1. Oligomerization of Ethylene by 6a,b at 26 °C, 400 psi in CH2Cl2 entry

catalysta

time, h

mg oligomers

TOF, h-1

Mnb

1 2 3 4

6a 6a 6b 6b

3 15 3 15

19 76 79c 270c

23 18 94 65

670 590 300 230

a 0.01 mmol of catalyst in 100 mL of CH Cl used. b M deter2 2 n mined by 1H NMR spectroscopy (see Experimental Section for c details). Butene, hexene, and octene fractions partially lost during evaporation of solvent (GC analysis).

the difference in insertion barriers accounts for the observed difference in TOF (Pd diimines: ca. 4500 TO/ h;3e 6b, 94 TO/h at RT).

2. Palladium(II) Catalysts Containing Phosphinidine-Sulfide Ligands. Since the oligomerizations using phosphinidine-imine palladium complexes were relatively slow, we decided to examine other chelating ligand-palladium complexes incorporating the phosphinidine moiety. The use of phosphine-phosphinidine palladium complex 8 (geometry around Pd arbitrary) was not successful (butenes were produced at 1 atm C2H4 in an NMR experiment). Modification of this structure was problematic due to the instability of the ligand and synthetic intermediates (high air and moisture sensitivity, low crystallinity). As a consequence, we

turned to the investigation of phosphinidine-sulfidebased catalysts. Initially, two ligands possessing bulky substituents on sulfur were synthesized using phosphaPetersen methodology developed by Yoshifuji et al.12 The reaction of the potassium salt of tri-isopropylthiophenol with bromoacetaldehyde diethyl acetal followed by acidic hydrolysis afforded tri-isopropylphenylthioacetaldehyde 9. The aldehyde was then treated with Mes*P(Li)TBS to give a 100:8 mixture of phosphinidine isomers. Crude phosphinidine was converted into the corresponding complex 10a by treatment with (cod)PdMeCl. Chloride abstraction with Na(BArF)4 in the presence of acetonitrile afforded the cationic complex 11a. In a similar way, complex 11b was obtained starting from the known R-tert-butylthioacetaldehyde (Scheme 3).13 The reactions of ethylene with cationic complexes 11a,b were initially studied by NMR spectroscopy using 20 equiv of olefin and 0.01 mmol of catalyst in CD2Cl2. Under these conditions tert-butyl-substituted complex 11b produces a mixture of internal butenes. Interestingly, the major component was cis-2-butene (2:1). Gratifyingly, tri-isopropylphenyl-substituted catalyst 11a afforded ethylene oligomers in a relatively fast reaction. In 3 h under 400 psi of ethylene, 0.01 mmol of 11a produced 3.6 g of oligomers (corresponding to 4300 TO/h) with Mn ) 215. In a 15 h run, TOF dropped to 3000 h-1, showing some catalyst decomposition (Table 2). Compared to diimine-Pd complexes, 11a displays higher stability and produces lower molecular weight material. In an effort to increase the molecular weight of the oligomer/polymer produced, catalyst 14 was designed and synthesized (Scheme 4). Geminal dimethyl groups on the chelate backbone should impart a more restricted conformation to the S-aryl group, possibly leading to more efficient blocking of the axial sites on the metal and potentially higher molecular weight material. The synthesis started with the reaction of tri-isopropylphenylsulfenyl chloride14 with the potassium enolate of isobutyraldehyde to give the corresponding R-thioaldehyde 12.15 The conversion to the cationic palladium complex 14 was carried out as in the case of 11. Under 400 psi of ethylene, 14 produced highly branched (119 br/1000 C) polyethylene with Mn ) 23002500, PDI ) 1.5, consistent with a single-site catalyst (12) Yoshifuji, M.; Toyota, K.; Matsuda, I.; Niitsu, T.; Inamoto, N. Tetrahedron Lett. 1985, 26, 1727. (13) Kudzin, Z. H. Synthesis 1981, 643. (14) Garratt, D. G.; Beaulieu, P. L. Can. J. Chem. 1980, 58, 2737. (15) Groenewegen, P.; Kallenberg, H.; van der Gen, A. Tetrahedron Lett. 1979, 20, 2817.

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Daugulis et al. Scheme 3

Figure 3. ORTEP view of 10a. Selected interatomic distances (Å) and torsion angles (deg): P(1)-Pd(1) ) 2.1920(7), S(1)-Pd(1) ) 2.3965(7), Pd(1)-C(1) ) 2.046(3), Pd(1)-Cl(1) ) 2.3496(7), P(1)-C(2) ) 1.652(3), S(1)-C(3) ) 1.826(3), C(34)-C(18) ) 5.130(4); P(1)-Pd(1)-S(1)-C(3) 13.96(15). Scheme 4

(Table 2). The observed TOF for a 3 h run was 3100 h-1, for an 8 h run 2300 TO/h. Remarkably, introduction of the geminal dimethyl groups has increased the molecular weight of the polymer more than 10 times. To investigate the origin of this effect, single-crystal X-ray structures were obtained for the complexes 10a and 13 (Figures 3 and 4). The geometries of these complexes were thought to approximate the geometries of the active species in the polymerization reaction. The CdP bond lengths (1.659(3) Å for 13 and 1.653 Å for 10a) are typical for phosphinidine-palladium complexes.6a,9 The Pd-P bonds (2.2071(8) Å for 13, 2.1920(7) Å for 10a) are slightly longer than observed for 6a. As expected from the small magnitude of CH3-31P coupling constants (see Experimental Section for details), the methyl group is positioned cis to phosphinidine. The palladium-sulfur bond is somewhat longer in 13 compared to 10a (2.4277(8) vs 2.3965(7) Å). In 13, the five-membered chelate ring is planar within 2 degrees; in 10a it adopts an envelope conformation with the sulfur atom forming the flap of the envelope (torsion angle P(1)-Pd(1)-S(1)-C(3) ) 13.96(15)°). The C(34)-C(18) distance in 10a is 5.130(4) Å; in 13 the corresponding C(23)-C(37) distance is

Figure 4. ORTEP view of 13. Selected interatomic distances (Å) and angles (deg): P(1)-Pd(1) ) 2.2071(8), S(1)Pd(1) ) 2.4277(8), Pd(1)-C(1) ) 2.047(3), Pd(1)-Cl(1) ) 2.3475(8), P(1)-C(3) ) 1.659(3), S(1)-C(2) ) 1.891(3), C(23)-C(37) ) 4.693(4), C(11)-S(1) ) 1.808(3); C(34)C(31)-P(1) ) 169.04(17). Table 3. Comparison of Polyethylene Branching Obtained Using 14a and [((2,6-Me2C6H3)NdC(Me)C(Me)dN(2,6-Me2C6H3))Pd(CH2)3C(O)OMe]BArF4 (15)16 catalyst

Meb

Et

14 % Mee 15f % Mee

39.0 31.7 41.5 36.4

29.7 24.1 23.1 20.3

Pr

nBu sBu Am higher br/1000 Cc

5.2 16.7 6.7d 4.2 13.6 4.4 9.3 6.1d 3.9 8.2

8.8 7.2 4.6 4.0

23.6 19.2 31.9 28.0

123 114

a Reaction under the conditions of Table 2. b Number of corresponding branches per 1000 C. c Total number of methyl branches per 1000 C. d A sBu branch is counted as one Me and one Et branch. e Percent of the methyl groups in the given branch with respect to total Me. f Data from ref 16, 500 psi ethylene pressure, 35 °C reaction temperature, chlorobenzene solvent.

4.693(4) Å, leading to a more efficient blocking of one axial coordination site in the second case. Another interesting feature of 13 is the deformation of the P-aryl moiety, perhaps due to unfavorable steric interaction of the 2-tert-butyl group with the isopropyl substituent. The deformation results in a C(34)-C(31)-P(1) angle of 169.04(17)° (reflecting the bending at C(31)). Additionally in 13 the nonbonding interactions of the geminal methyl groups with the isopropyl substituent are expected to restrict the conformational mobility of the S-aryl group, leading to more efficient shielding of the lower axial coordination site on palladium. Analysis of the nature of the branching using 13C spectroscopy16 showed that the polymer is hyperbranched, with methyl to amyl branches identified and quantified (Table 3). The distribution of branches is somewhat different from that observed for polyethylene (16) Cotts, M. P.; Guan, Z.; McCord, E.; McLain, S. Macromolecules 2000, 19, 6945.

Phosphinidine-Palladium Complexes

produced from palladium-diimine catalysts.16 The polymer formed by 14 has somewhat fewer methyl branches (39.0/1000 C compared to 41.5/1000 C) and substantially more n-butyl branches (16.7 nBu/1000 C compared to 9.3 nBu/1000 C). The total number of branches calculated from 13C spectral analysis (123/1000 C) agrees with the branching number obtained from the 1H spectrum (119/1000 C). 3. Palladium(II) Catalysts Containing ImineSulfide Ligands. The replacement of an imine with a phosphinidine moiety in these catalysts decreased the molecular weight of ethylene polymerization products (compare 1 and 6a,b). As a consequence, an interesting modification was the replacement of phosphinidine in phosphinidine-sulfide ligands with an imine functionality, leading to the structure 18. A few imine-sulfide palladium and nickel catalysts have been described in patent literature.17 The reaction of 12 with 2,6-diisopropylaniline afforded the corresponding imine. The complexation with palladium was more difficult than in the case of phosphinidines. Sulfide-imine ligand 16 did not displace cod from (cod)PdMeCl completely. To obtain complete conversion to 17, azeotropic removal of cyclooctadiene from the equilibrium mixture was necessary. Conversion to 18 was carried out as in the case of phosphinidines.

Organometallics, Vol. 21, No. 26, 2002 5939

polymerization conditions than the corresponding imine complexes; even after 15 h at RT phosphinidine-sulfide catalyst 11a displays a turnover rate of 3000 TO/h, while for a 3 h run the TOF was determined to be 4300 h-1. A new method of blocking axial sites on metal by restricting the conformational mobility of the sulfide ligand using gem-dimethyl substituents on the fivemembered chelate ring backbone has also been developed, resulting in a 10-fold molecular weight increase of the polymer. Polyethylene obtained using phosphinidine-sulfide catalyst 14 is extremely highly branched (119 br/1000 C). Experimental Section

Several new cationic phosphinidine-imine, phosphinidine-sulfide, and imine-sulfide palladium(II) complexes have been prepared. The complexes display moderate to high activity (for palladium complexes) in the oligomerization and polymerization of ethylene. Phosphinidine-containing catalysts are more stable under the

General Considerations. All the operations related to catalysts or phosphines were carried out under an argon atmosphere using standard Schlenk techniques. The 1H, 31P, and 13C spectra were recorded using Bruker 300 or 400 MHz spectrometers and referenced against residual solvent peaks (1H, 13C) or H3PO4 (31P). Flash chromatography was performed using 60 Å silica gel (SAI). Room-temperature GPC measurements were performed on a Waters Alliance HPLC separations module equipped with Waters Styragel HR2, HR4, and HR5 columns in series and a Waters 2410 differential refractometer RI (refractive index) detector relative to polystyrene standards. Samples consisted of ∼1 mg of polymer in 1 mL of degassed THF. Universal calibration was applied using Mark-Houwink constants for polyethylene (k ) 4.34 × 10-4; R ) 0.724). Elemental analyses were performed by Atlantic Microlab Inc. of Norcross, GA. 13C NMR analysis of polymer obtained with 14 was carried out under the conditions reported by the DuPont group.16 Materials. Anhydrous solvents were used in the reactions. Solvents were distilled from drying agents or passed through alumina columns under an argon or nitrogen atmosphere. NMR solvents were vacuum transferred from P2O5 and degassed by repeated freeze-pump-thaw cycles. The following starting materials were made using literature procedures: Mes*PCl2,18 Mes*PH2,18 (cod)PdMeCl,7 2,4,6-tri-isopropylthiophenol,19 R-tert-butylthioacetaldehyde,13 and 2,4,6-tri-isopropylphenylsulfenyl chloride.14 NaB(ArF)4 was purchased from Boulder Scientific. Analysis of Polymer Molecular Weight and Branching by 1H NMR Spectroscopy. The following labels are used for denoting different types of hydrogen signals in the polymer spectrum (CDCl3 solvent): H1 (vinylidene end group, CdCH2, br s, 4.7 ppm); H2 (1,2-disubstituted olefin, CHdCH, m, 5.35.4 ppm); H3 (trisubstituted olefin CdCH, m, 5.18 ppm); H4 (R-olefin, H2CdCH, m, 5.85, 5.0, 4.9 ppm); H5 (alkyl methyl, alk-CH3, m, 0.77-0.95 ppm); H6 (allylic methyl, CdC-CH3, m, 1.6 ppm); H7 (alkyl methylene and methine, alk-CH and alk-CH2, m, ca. 1.0-1.45 ppm); H8 (allylic methylene or methine, CdC-CH2 and CdC-CH, m, 1.85-2.05 ppm). In the following formulas Hn’s refer to integral values. Nav ) (2/V)(A) + 2, where Nav ) average number of carbons in polymer chain, V ) H1 + H2 + 2H3 + (2/3)H4, and A ) (H5 + H6 + H7 + H8 - H1 - H2 - 3H3 - (1/3)H4)/2 Mn ) (Nav)14.01 Nbr ) (1000/Nav)(Y - X) where Nbr ) number of methyl branches per 1000 C, Y ) ((H5 + H6)/3)(2/V), and X ) ((H1/2) + H2 + 2H3 + (H4/3))*(2/V). The formula is not exact since the signal of the secondary homoallylic hydrogen overlaps with the signal of H6.

(17) Al-Ahmad, S. WO 01/87996 A2, 2001. Several examples of ethylene polymerization using cationic imine-sulfide Pd complexes are described in this patent. Polyethylene with Mn of 200-700 was obtained.

(18) Cowley, A. H.; Norman, N. C.; Pakulski, M. Inorg. Synth. 1990, 27, 235. (19) Costanza, A. J.; Coleman, R. J.; Pierson, R. M.; Marvel, C. S.; King, C. J. Polym. Sci. 1955, 17, 319.

In an NMR experiment (20 equiv of ethylene, 0.01 mmol of cat., CD2Cl2 solvent) catalyst 18 rapidly consumed ethylene. A preparative run under 1 atm of ethylene (0.01 mmol of cat., 100 mL of CH2Cl2) afforded 146 mg of polyethylene (Mn ) 2800) in 44 h. Under 400 psi ethylene, only a small amount (54 mg/3 h; 72 mg/15 h, 0.01 mmol 18) of polyethylene with Mn ) 1800 was obtained. Since the 400 psi experiment afforded less polyethylene than the 1 atm run, it is possible that under high pressure of ethylene the ligand is displaced from the palladium, resulting in the decomposition of the catalyst (precipitation of palladium black was observed). Summary

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Spectral Data for the B(ArF)4 Counterion. The following H and 13C spectroscopic assignments of the B(ArF)4 counterion were invariant for different complexes and temperatures and are not reported in the spectroscopic data for each of the cationic complexes. B[3,5-C6H3(CF3)2]4- (B(ArF)4). 1H NMR (CD2Cl2): 7.74 (br s, 8H), 7.57 (s, 4H). 13C{1H} NMR (CD2Cl2): 162.2 (q, JC-B ) 37.4 Hz), 135.2, 129.3 (q, JC-F ) 31.3 Hz), 125.0 (q, JC-F ) 272.5 Hz), 117.9. General Polymerization Procedure. Polymerizations were carried out in a mechanically stirred 300 mL Parr reactor equipped with an electric heating mantle controlled by a thermocouple in the reaction mixture. The reactor was charged with toluene (100 mL) and heated for 1 h at 150 °C. After cooling to RT the solvent was poured out and the reactor heated under vacuum at 150 °C for 1 h. The reactor was filled with Ar, cooled to RT, pressurized to 200 psi ethylene, and vented three times. A solution of the catalyst in 100 mL of CH2Cl2 was added to the reactor via cannula, the reactor pressurized with ethylene to 400 psig, and the pressure maintained at this value during the polymerization. After that the reaction mixture was stirred for the appropriate time. Observed exotherms were always less than 2 °C, and the polymerizations were run at 26 °C. After venting the reaction mixture was evaporated and the distillate checked for oligomers by GC. Propiophenone 2,6-Di-isopropylphenylimine, 3a. 2,6Diisopropylaniline (3.8 mL, 20 mmol, Aldrich) was mixed with propiophenone (2.7 mL, 20 mmol, Aldrich) and p-TsOH (0.4 g, 2.1 mmol, Aldrich). The resulting mixture was heated at 205 °C for 1.5 h under a weak stream of Ar to remove formed H2O. After cooling to RT the reaction mixture was poured into hexanes (50 mL) and filtered, and the precipitate was washed with additional hexanes (2 × 20 mL) followed by the evaporation of the filtrate and distillation of the residue. After the initial fraction of starting materials (80-110 °C/0.5 mm) the product was collected as a yellow oil, bp 110-125 °C/0.5 mm. Crystallization from methanol at -30 °C afforded the product as yellow crystals (4.3 g, 73.3%). 1H NMR (CDCl3): 7.99-7.91 (m, 2H); 7.54-7.44 (m, 3H); 7.20-7.13 (m, 2H); 7.12-7.04 (m, 1H); 2.78 (septet, 2H; J ) 6.9 Hz); 2.53 (q, 2 H; J ) 7.7 Hz); 1.21 (d, 6 H; J ) 6.9 Hz); 1.16 (d, 6 H; J ) 6.9 Hz); 0.99 (t, 3 H; J ) 7.7 Hz). 13C{1H} NMR (CDCl3): 169.9, 146.6, 138.2, 136.1, 130.3, 128.7, 127.9, 123.4, 123.0, 28.4, 24.3, 23.7, 22.7, 11.4. Anal. Calcd for C21H27N: C 85.95, H 9.27, N 4.77. Found: C 86.05, H 9.32, N 4.79. Propiophenone 2,4,6-Trimethylphenylimine, 3b. 2,4,6Trimethylaniline (11.5 mL, 82 mmol, Aldrich) was mixed with propiophenone (10 mL, 74.5 mmol, Aldrich) and p-TsOH (1.4 g, 7.3 mmol, Aldrich). The resulting mixture was heated for 2 h at 200 °C under a weak stream of Ar to remove formed H2O. After cooling to RT the reaction mixture was poured into hexanes (100 mL) and filtered, and the precipitate washed with additional hexanes (2 × 100 mL) followed by the evaporation of the filtrate. The residue was filtered through a 9 × 4.1 cm plug of silica gel in 10:1 hexanes/ether (300 mL collected). After evaporation of the solvent the unreacted starting materials were distilled off under vacuum (45-50 °C/0.4 mm). The residue was crystallized from methanol at -30 °C. Product was isolated as large orange-yellow crystals, 4.8 g (25.6%). 1H NMR (CDCl3): 8.00-7.94 (m, 2H); 7.51-7.45 (m, 3H); 6.89 (s, 2H); 2.50 (q, 2H; J ) 7.7 Hz); 2.31 (s, 3H); 2.04 (s, 6H); 0.98 (t, 3H; J ) 7.7 Hz). 13C{1H} NMR (CDCl3): 170.8, 146.4, 138.2, 131.9, 130.3, 128.7, 128.6, 127.7, 125.6, 23.9, 20.9, 18.2, 11.6. Anal. Calcd for C18H21N: C 86.00, H 8.42, N 5.57. Found: C 85.79, H 8.41, N 5.56. (2,6-(i-Pr)2C6H3)NdC(Ph)C(Me)dPMes*, 4a. nBuLi (3.3 mL of a 1.6 M solution in hexanes, 5.25 mmol, Aldrich) was added to a solution of diisopropylamine (0.77 mL, 5.5 mmol, Aldrich) in THF (5 mL) at -78 °C. The solution was stirred

1

Daugulis et al. for 10 min at -78 °C followed by the addition of a solution of propiophenone 2,6-diisopropylphenylimine (1.47 g, 5 mmol) in THF (7 mL). The cooling bath was removed, and the reaction mixture was stirred for 3 h at RT. The solution of lithium azaenolate was added dropwise to a solution of 2,4,6-tri-tertbutylphenyldichlorophosphine (1.77 g, 5 mmol; contained some ArPBrCl) in THF (10 mL) at -78 °C. The reaction mixture was warmed to RT and stirred for 1 h. Assay by 31P NMR showed the presence of ArP(Cl)R (+99.8 ppm). The solvent was evaporated under Ar, and dry DBU (1,8-diazabicyclo[5.4.0]undec-7-ene, 1.5 mL, 10 mmol, Aldrich) was added, followed by dry CH3CN (7 mL). The mixture was heated in a sealed Kontes flask at 90 °C for 3 h. Assay by 31P NMR showed the presence of product and chloro (or bromo)phosphine in a 2.5:1 ratio (+304.0, +87.2 ppm) together with some unidentified decomposition products. The solvent was evaporated and the residue filtered through a 10 × 3.3 cm silica gel column in toluene, collecting the red-yellow product band. After evaporation the residue was recrystallized from CH3CN twice at -30 °C to give product as red-yellow crystals, 0.88 g (31.0%). Rf ) 0.53 (1:1 toluene/hexane). 1H NMR (C6D6): 7.60 (s, 2H); 7.467.39 (m, 2H); 7.07-6.85 (m, 6H); 3.12 (septet, 2H; J ) 6.8 Hz); 2.09 (d, 3H; J ) 12.5 Hz); 1.54 (s, 18H); 1.34 (s, 9H); 1.23 (d, 6H, J ) 6.8 Hz); 1.13 (d, 6H, J ) 6.8 Hz). 13C{1H, 31P} NMR (CDCl3): 184.5; 169.0; 153.4; 150.5; 146.7; 137.7; 137.6; 135.4; 129.0; 128.6; 127.9; 127.4; 123.0; 122.4; 122.1; 38.1; 35.2; 32.7; 31.6; 28.8; 23.9; 22.0; 21.7. 31P{1H} NMR (C6D6): +303.0 ppm. Anal. Calcd for C39H54NP: C 82.49, H 9.59, N 2.47. Found: C 82.28, H 9.73, N 2.43. MesNdC(Ph)C(Me)dPMes*, 4b. nBuLi (2.3 mL of a 1.6 M solution in hexanes, 3.7 mmol, Aldrich) was added to a solution of diisopropylamine (0.54 mL, 3.85 mmol, Aldrich) in THF (10 mL) at -78 °C. The solution was stirred for 10 min at -78 °C followed by the addition of a solution of propiophenone 2,4,6-trimethylphenylimine (0.88 g, 3.51 mmol) in THF (15 mL). The cooling bath was removed, and the reaction mixture was stirred for 3 h at RT. The solution of lithium azaenolate was added dropwise to a solution of 2,4,6-tri-tertbutylphenyldichlorophosphine (1.24 g, 3.57 mmol; contained some ArPBrCl) in THF (10 mL) at -78 °C. The reaction mixture was warmed to RT and stirred for 1 h. Assay by 31P NMR showed the presence of ArP(Cl)R (+90.3 ppm). Dry DBU (1.1 mL, 7.36 mmol, Aldrich) was added. After 2 h, assay by 31 P NMR showed no reaction. The solvent was evaporated under vacuum, and dry CH2Cl2 (10 mL) and dry CH3CN (10 mL) were added. The mixture was stirred at RT for 15 h 30 min. Assay by 31P NMR (crude reaction mixture) showed the presence of product isomers in a 100:4 ratio (+306.7; +279.3 ppm). The solvent was evaporated and the residue filtered through a 16 × 3.3 cm silica gel plug in CH2Cl2, collecting 100 mL. After evaporation the residue was recrystallized from dry CH3CN at -30 °C to give product as yellow crystals, 1.04 g (57.0%). 1H NMR (CDCl3): 7.46 (s, 2H); 7.28-7.12 (m, 5H); 6.64 (s, 2H); 2.13 (s, 3H); 1.96 (s, 6H); 1.70 (d, 3H; J ) 12.4 Hz); 1.47 (s, 18H); 1.36 (s, 9H). 13C{1H, 31P} NMR (CDCl3): 183.9; 170.7; 153.3; 150.6; 146.6; 138.4; 137.6; 131.5; 128.6; 128.4; 128.3; 127.4; 125.1; 122.1; 38.1; 35.2; 32.7; 31.6; 21.6; 20.9; 18.6. 31P{1H} NMR (CDCl3): +307.0 ppm. Anal. Calcd for C36H48NP: C 82.24, H 9.20, N 2.66. Found: C 82.11, H 9.32, N 2.67. [(2,6-(i-Pr)2C6H3)NdC(Ph)C(Me)dPMes*]PdMeCl, 5a. (Cod)PdMeCl (0.047 g, 0.176 mmol) was mixed with 4a (0.10 g, 0.176 mmol) and CH2Cl2 (3 mL). The yellowish solution was stirred for 14 h at RT. After evaporation the residue was triturated with hexanes (3 mL). The hexanes were evaporated, and the residue was dried under vacuum to give 5a as a reddish solid (0.109 g, 85.4%). 1H NMR (CDCl3): 7.62 (d, 2H; J ) 3.3 Hz); 7.22-7.14 (m, 3H); 7.09-6.94 (m 3H); 6.92-6.83 (m, 2H); 3.00 (septet, 2H; J ) 6.8 Hz); 1.69 (d, 18H; J ) 0.7 Hz); 1.47 (d, 6H; J ) 6.8 Hz); 1.36 (s, 9H); 1.26 (Pd-Me; d, 3H;

Phosphinidine-Palladium Complexes J ) 4.2 Hz); 1.18 (d, 3H; J ) 26.0 Hz); 1.00 (d, 6H; J ) 6.8 Hz). 31P{1H} NMR (CDCl3): +268.3 ppm. Anal. Calcd for C40H57ClNPPd: C 66.29, H 7.93, N 1.93. Found: C 66.20, H 8.01, N 1.91. [MesNdC(Ph)C(Me)dPMes*]PdMeCl, 5b. The synthesis was performed as in the case of 5a, using 4b (0.200 g, 0.38 mmol) and (cod)PdMeCl (0.101 g, 0.38 mmol) in CH2Cl2 (5 mL). The product was isolated as a reddish solid (0.23 g, 88.7%). 1H NMR (CD Cl ): 7.65 (d, 2H; J ) 3.3 Hz); 7.27-7.17 (m, 2 2 3H); 6.99-6.90 (m, 2H); 6.69 (s, 2H); 2.19 (s, 6H); 2.18 (s, 3H); 1.69 (d, 18H; J ) 1.1 Hz); 1.37 (s, 9H); 1.12 (Pd-Me; d, 3H; J ) 4.4 Hz); 1.11 (d, 3H; J ) 26.3 Hz). 13C{1H} (CD2Cl2) 176.8 (d, JC-P ) 11.1 Hz); 163.5 (d, JC-P ) 45.8 Hz); 157.0; 155.4 (d, JC-P ) 2.4 Hz); 144.8 (d, JC-P ) 3.3 Hz); 135.6 (d, JC-P ) 10.9 Hz); 134.8; 129.6; 129.5 (d, JC-P ) 4.1 Hz); 128.6; 128.1; 126.3; 124.4 (d, JC-P ) 8.0 Hz); 121.0 (d, JC-P ) 3.5 Hz); 39.4; 35.9; 33.7 (d, JC-P ) 1.4 Hz); 31.1; 22.1 (d, JC-P ) 11.7 Hz); 21.1; 19.4; 2.0 (Pd-Me; d, JC-P ) 2.9 Hz). 31P{1H} NMR (CD2Cl2): +267.3 ppm. Anal. Calcd for C37H51ClNPPd: C 65.09, H 7.53, N 2.05. Found: C 64.96, H 7.53, N 2.08. [((2,6-(i-Pr)2C6H3)NdC(Ph)C(Me)dPMes*)Pd(NCMe)Me]+B(ArF)4-, 6a. To the mixture of 5a (prepared from 0.176 mmol of 4a, 0.176 mmol of (cod)PdMeCl) and NaB(ArF)4 (0.156 g, 0.176 mmol) were added dry acetonitrile (1 mL) and CH2Cl2 (3 mL). The mixture was stirred for 1 h at RT, cannula filtered to remove NaCl, evaporated, and coevaporated with hexanes (3 mL). The product was obtained as a reddish solid (0.270 g, 96.3%). X-ray quality crystals were obtained by crystallization from warm toluene. 1H NMR (CD2Cl2): 7.70 (d, 2H; J ) 4.0 Hz); 7.36-7.28 (m, 3H); 7.18-7.08 (m, 3H); 6.986.93 (m, 2H); 2.94 (septet, 2H; J ) 6.8 Hz); 1.75 (s, 3H); 1.67 (d, 18 H; J ) 1.3 Hz); 1.4 (d, 6H; J ) 6.8 Hz); 1.37 (s, 9H); 1.36 (d, 3H; J ) 29.3 Hz); 1.09 (d, 6H; J ) 6.8 Hz); 1.03 (PdMe; d, 3H; J ) 2.6 Hz). 31P{1H} NMR (CD2Cl2): +267.4 ppm. Anal. Calcd for C74H72BF24N2PPd: C 55.77, H 4.55, N 1.76. Found: C 55.48, H 4.42, N 1.73. [(MesNdC(Ph)C(Me)dPMes*)Pd(NCMe)Me]+B(ArF)4-, 6b. The synthesis was performed as in the case of 6a, using 4b (0.100 g, 0.19 mmol), (cod)PdMeCl (0.050 g, 0.19 mmol), and NaB(ArF)4 (0.169 g, 0.19 mmol). Product was obtained as a reddish powder, 0.292 g (100%). 1H NMR (CD2Cl2): 7.69 (d, 2H; J ) 3.9 Hz); 7.37-7.23 (m, 3H); 7.00-6.94 (m, 2H); 6.80 (s, 2H); 2.22 (s, 6H); 2.19 (s, 3H); 1.74 (s, 3H); 1.66 (d, 18H; J ) 1.3 Hz); 1.37 (s, 9H); 1.30 (d, 3H; J ) 29.4 Hz); 1.02 (PdMe; d, 3H; J ) 2.6 Hz). 13C{1H} NMR (CD2Cl2): 177.8 (d, JC-P ) 8.0 Hz); 167.5 (d, JC-P ) 54.4 Hz); 157.5 (d, JC-P ) 1.8 Hz); 157.1 (d, JC-P ) 2.9 Hz); 143.9 (d, JC-P ) 3.7 Hz); 136.6; 133.6 (d, JC-P ) 10.7 Hz); 130.9; 129.2; 129.1 (d, JC-P ) 2.4 Hz); 126.4; 125.1 (d, JC-P ) 9.3 Hz); 120.5; 117.5 (d, JC-P ) 15.3 Hz); 39.5 (d, JC-P ) 1.7 Hz); 36.0; 33.9; 31.2; 22.6 (d, JC-P ) 11.3 Hz); 20.9; 19.0; 3.8 (Pd-Me; d, JC-P ) 2.7 Hz); 2.0. One aromatic carbon is unaccounted for. 31P{1H} NMR (CD2Cl2): +266.0 ppm. Anal. Calcd for C71H66BF24N2PPd: C 54.96, H 4.29, N 1.80. Found: C 55.32, H 4.63, N 1.78. Generation of [(MesNdC(Ph)C(Me)dPMes*)Pd(ethylene)Me]+B(ArF)4-, 7. Measurement of Ethylene Insertion Barrier. Solid 5b (0.0068 g, 0.01 mmol) was mixed with NaB(ArF)4 (0.012 g, 0.014 mmol) in a Teflon-lined screw-cap NMR tube. After cooling to -78 °C ethylene (1 mL, 0.045 mmol) was added, followed by CD2Cl2 (0.7 mL) and more ethylene (4 mL, 0.18 mmol). The NMR tube was placed in an NMR probe at 250 K, and the disappearance of the methyl peak (0.95 ppm) of the formed methyl ethylene complex was observed vs time, affording k ) 7.9 × 10-5 s-1, corresponding to ∆Gq ) 19.2(1) kcal/mol. After the disappearance of the methyl peak, additional ethylene (5 mL, 0.22 mmol) was added and the disappearance of the ethylene peak was measured with respect to time, affording k ) 2.4 × 10-4 s-1, ∆Gq ) 18.7(1) kcal/mol. The error was derived from the error in the rate constant, which in turn was obtained by the least-squares fit of the kinetic data.

Organometallics, Vol. 21, No. 26, 2002 5941 Spectral Data for 7. 31P{1H} NMR (CD2Cl2, 233 K): +255.6 ppm. 1H NMR (CD2Cl2, 243 K): 7.65 (d, 2H; J ) 3.7 Hz); 7.35-7.21 (m, 3H); 6.94-6.87 (m, 2H); 6.80 (s, 2H); 2.17 (s, 3H); 2.15 (s, 6H); 1.60 (s, 18H); 1.35 (d, 3H; J ) 29.0 Hz); 1.32 (s, 9H); 0.95 (Pd-Me; d, 3H; J ) 3.7 Hz). Complexed ethylene exchanges with excess free ethylene fast even at 193 K, resulting in coalescence of NMR signals (5.37 ppm at 243 K and 22 equiv of ethylene). (2,4,6-Tri-isopropylphenylthio)acetaldehyde, 9. To a solution of 2,4,6-tri-isopropylthiophenol (8.0 g, 33.9 mmol) in THF (130 mL) was added KHMDS (74.5 mL of a 0.5 M toluene solution, 37.3 mmol, Aldrich) at 0 °C and the resulting mixture stirred for 30 min at 0 °C. Bromoacetaldehyde diethylacetal (5.6 mL, 37.3 mmol, Aldrich) was added dropwise to the solution of the potassium thiolate at 0 °C. The ice bath was removed and the reaction mixture stirred for 4 h at RT. After that, it was poured into H2O (300 mL) and extracted with diethyl ether (3 × 200 mL). Extracts were then dried (MgSO4), filtered, and evaporated (aspirator). The crude reaction mixture was refluxed with 2% aqueous HCl (60 mL) and acetone (100 mL) for 2 h. The reaction mixture was poured into saturated aqueous sodium bicarbonate solution and extracted with diethyl ether (2 × 200 mL), and the extracts were dried (MgSO4), filtered, and evaporated. Distillation of the product gave a clear liquid, bp 108-113 °C/0.5 mm, 5.79 g (61.4%). The compound slowly decomposes at RT and needs to be stored in the freezer. 1H NMR (C6D6): 9.57 (t, 1H; J ) 3.4 Hz); 7.00 (s, 2H); 3.96 (septet, 2H; J ) 7.0 Hz); 2.81 (d, 2H; J ) 3.4 Hz); 2.70 (septet, 1H; J ) 7.0 Hz); 1.21 (d, 12H; J ) 7.0 Hz); 1.13 (d, 6H; J ) 7.0 Hz). 13C{1H} NMR (CDCl3): 193.3; 154.0; 151.1; 127.2; 122.8; 47.5; 35.0; 32.3; 24.9; 24.4. Anal. Calcd for C17H26OS: C 73.32, H 9.41. Found: C 73.38, H 9.50. Mes*P(Li)TBS.6b nBuLi (2.6 mL of a 1.6 M solution in hexanes, 4.2 mmol, Aldrich) was added to a solution of 2,4,6tri-tert-butylphenylphosphine (1.11 g, 4 mmol) in THF (30 mL) at -78 °C. The yellow suspension was stirred at -78 °C for 10 min, warmed to RT, and stirred for additional 15 min. A dark red solution was formed. Next, a solution of TBSCl (tertbutyldimethylsilyl chloride, 0.63 g, 4.2 mmol, Aldrich) in THF (10 mL) was added to ArPHLi over 10 min at 0 °C. The resulting yellowish solution was stirred at 0 °C for 20 min, warmed to RT, and stirred for 30 min. Assay by 31P NMR showed clean formation of ArPHTBS (-135.5 ppm). After cooling to -78 °C additional nBuLi (2.6 mL of a 1.6 M solution in hexanes, 4.2 mmol, Aldrich) was added, and the solution was immediately warmed to RT to give a reddish solution of ArP(Li)TBS that was used in the phosphinidine synthesis. [(2,4,6-(i-Pr)3C6H2)SCH2CHdPMes*]PdMeCl, 10a. A solution of (2,4,6-tri-isopropylphenylthio)acetaldehyde (0.835 g, 3.0 mmol) in THF (10 mL) was dropwise added to a solution of ArP(TBS)Li prepared as above (3.15 mmol scale) at -78 °C. The reaction color changed from red to yellow at the end of the reaction. After stirring for 30 min at -78 °C the reaction was warmed to RT and stirred for 1 h. TMSCl (0.3 mL) was then added to quench TBSOLi. Assay by 31P NMR showed the presence of phosphinidine isomers in the ratio of 100:8 (+262.5; +254.1 ppm). The solution was evaporated, CH2Cl2 (10 mL) was added followed by (cod)PdMeCl (0.670 g, 2.53 mmol), and the reaction mixture was stirred for 12 h at RT. The solution was evaporated and the residue purified by flash chromatography on silica gel (7.5 × 3.7 cm). Initially cod, ArPH2, and a minor phosphinidine diastereomer were eluted with hexanes (300 mL). After that, a dark red impurity was eluted with toluene (475 mL). Then, product was eluted with CH2Cl2 (400 mL). Fractions containing 10a were evaporated and crystallized from acetonitrile (50 mL) at -30 °C. Product was obtained as a light yellow, somewhat light sensitive solid, 0.60 g (28.7%). 1H NMR (CD2Cl2): 7.61 (d, 2H; J ) 3.5 Hz); 7.37 (dt, 1H; J ) 19.8, 4.2 Hz); 7.14 (s, 2H); 3.96 (septet, 2H; J ) 6.8 Hz); 3.56 (dd, 2H; J ) 40.4; 4.2 Hz); 2.94 (septet, 1H: J ) 6.9 Hz); 1.67 (s, 18H); 1.39 (d, 6H; J ) 6.8 Hz); 1.36 (s, 9H);

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1.31 (d, 6H; J ) 6.8 Hz); 1.29 (d, 6H; J ) 6.9 Hz); 1.15 (PdMe; d, 3H; J ) 4.1 Hz). 31P{1H} NMR (CD2Cl2): +237.6 ppm. Anal. Calcd for C36H58ClPPdS: C 62.14, H 8.40. Found: C 62.17, H 8.45. [((2,4,6-(i-Pr)3C6H2)SCH2CHdPMes*)Pd(NCMe)Me]+B(ArF)4-, 11a. To the mixture of 10a (0.129 g, 0.186 mmol) and NaB(ArF)4 (0.165 g, 0.186 mmol) were added dry acetonitrile (1 mL) and CH2Cl2 (3 mL). The mixture was stirred for 17 h at RT, cannula filtered to remove NaCl, evaporated, and coevaporated with hexanes (3 mL). The product was obtained as a reddish solid (0.250 g, 85.9%). 1H NMR (CD2Cl2): 7.65 (d, 2H; J ) 4.2 Hz); 7.48 (dt, 1H; J ) 19.4, 4.2 Hz); 7.19 (s, 2H); 3.88 (septet, 2H; J ) 6.8 Hz); 3.76 (dd, 2H; J ) 42.4; 4.2 Hz); 2.95 (septet, 1H; J ) 6.9 Hz); 2.00 (s, 3H); 1.64 (s, 18H); 1.36 (s, 9H); 1.33 (br d, 12H; J ) 6.8 Hz); 1.26 (d, 6H; J ) 6.9 Hz), 1.19 (Pd-Me; d, 3H; J ) 2.4 Hz). 31P{1H} NMR (CD2Cl2): +231.0 ppm. Anal. Calcd for C70H74BF24NPPdS: C 53.70, H 4.76, N 0.89. Found: C 53.88, H 4.88, N 0.80. t-BuSCH2CHdPMes*. A solution of (tert-butylthio)acetaldehyde (0.32 g, 2.4 mmol) in THF (7 mL) was added dropwise to a solution of 2,4,6-tri-tert-butylphenylP(TBS)Li prepared from 2,4,6-tri-tert-butylphenylphosphine (2 mmol) at -78 °C. The reaction color changed from red to yellow at the end of the reaction. After stirring for 30 min at -78 °C the reaction was warmed to RT. Assay by 31P NMR showed the presence of phosphinidine isomers in the ratio of 100:11 (+258.9; +252.8 ppm). TMSCl (0.3 mL) was added to quench TBSOLi, the solution was evaporated, and the residue was purified by flash chromatography on silica gel (14.5 × 3.3 cm) in 15:1 hexane/ toluene followed by 10:1. Fractions containing the major isomer were evaporated to give colorless oil that slowly crystallized. After recrystallization from dry acetonitrile at -30 °C colorless crystals (0.303 g, 38.6%) were obtained. Major diastereomer (trans) Rf ) 0.16 (15:1 hexane/toluene). Minor diastereomer (cis) Rf ) 0.25. The ligand is somewhat sensitive to water. 1H NMR (major diastereomer, CD2Cl2): 7.39 (d, 2H; J ) 0.9 Hz); 7.28 (dt, 2H; J ) 24.7, 9.2 Hz); 3.67 (dd, 2H; J ) 20.9, 9.2 Hz); 1.49 (s, 18H); 1.31 (s, 9H); 1.30 (s, 9H). 31P{1H} NMR (CD2Cl2): +258.0 ppm. Anal. Calcd for C24H41PS: C 73.41, H 10.51. Found: C 73.40, H 10.69. [t-BuSCH2CHdPMes*]PdMeCl, 10b. The synthesis was performed as in the case of 5a, using t-BuSCH2CHdPMes* (0.05 g, 0.127 mmol) and (cod)PdMeCl (0.034 g, 0.127 mmol). Product was obtained as an off-white solid, 0.058 g (83.1%). 1 H NMR (CDCl3): 7.54 (d, 2H; J ) 3.4 Hz); 7.45 (dt, 1H; J ) 19.0, 4.2 Hz), 3.29 (dd, 2H; J ) 40.0, 4.2 Hz); 1.62 (s, 9H); 1.58 (s, 18H); 1.33 (s, 9H); 1.23 (Pd-Me; d, 3H; J ) 3.7 Hz). 31 P{1H} NMR (CDCl3): +236.9 ppm. Anal. Calcd for C25H44ClPPdS: C 54.64, H 8.07. Found: C 54.88, H 8.10. [(t-BuSCH2CHdPMes*)Pd(NCMe)Me]+B(ArF)4-, 11b. The synthesis was performed as in the case of 6a, using t-BuSCH2CHdPMes* (0.100 g, 0.255 mmol), (cod)PdMeCl (0.068 g, 0.255 mmol), and NaB(ArF)4 (0.226 g, 0.255 mmol). Product was obtained as a reddish foam, 0.290 g (86.7%). 1H NMR (CD2Cl2): 7.62 (d, 2H; J ) 4.1 Hz); 7.59 (dt, 1H; J ) 18.3, 4.2 Hz); 3.44 (dd, J ) 42.1, 4.2 Hz); 2.37 (s, 3H); 1.56 (d, 18H; J ) 0.9 Hz); 1.54 (s, 9H); 1.34 (s, 9H); 1.14 (Pd-Me; d, 3H; J ) 2.3 Hz). 31P{1H} NMR (CD2Cl2): +229.3 ppm. Anal. Calcd for C59H59BF24NPPdS: C 49.96, H 4.19, N 0.99. Found: C 50.28, H 4.23, N 0.99. 2-Methyl-2-(2,4,6-tri-isopropylphenylthio)propanal, 12. To a suspension of KH (383 mg, 9.5 mmol, Aldrich; washed with hexanes to remove oil and dried in a vacuum) in THF (10 mL) was added dropwise isobutyric aldehyde (0.79 mL, 8.7 mmol, Aldrich) in THF (3 mL). The suspension was stirred for 25 min at RT under Ar (evolution of H2!). A solution of 2,4,6tri-isopropylphenylsulfenyl chloride (2.35 g, 8.7 mmol) in THF (10 mL) was then added in one portion. The color immediately changed from red to yellow. The solution was stirred at RT for 10 min, and water (20 mL) was added to the reaction mixture under Ar (caution: H2 evolution!). The solution was

Daugulis et al. extracted with diethyl ether (2 × 30 mL), and the extracts were dried (MgSO4), filtered, and evaporated. The residue was purified by flash chromatography on silica gel (13 × 4.3 cm) in 1:5 toluene/hexane followed by 1:4. Fractions containing the product were evaporated to give a light yellow oil that slowly crystallized, m ) 2.034 g (68.5%). Rf ) 0.33 (1:3 toluene/ hexane). 1H NMR (CDCl3): 9.34 (s, 1H); 7.00 (s, 2H); 3.85 (septet, 2H; J ) 6.9 Hz); 2.86 (septet, 1H; J ) 6.9 Hz); 1.29 (s, 6H); 1.24 (d, 6H; J ) 6.9 Hz); 1.18 (unresolved br d, 12H). 13C{1H} NMR (CDCl3, 333 K): 195.8; 155.2; 151.1; 123.7; 122.1; 55.7; 34.5; 32.3; 24.5; 24.0; 21.7. Anal. Calcd for C19H30OS: C 74.45, H 9.87. Found: C 74.52, H 9.98. [(2,4,6-(i-Pr)3C6H2)SCMe2CHdPMes*]PdMeCl, 13. A solution of 2-methyl-2-(2,4,6-tri-isopropylphenylthio)propanal (0.307 g, 1.0 mmol) in THF (5 mL) was added dropwise to a solution of ArP(TBS)Li prepared from 2,4,6-tri-tert-butylphenylphosphine (1.05 mmol) at -78 °C. The reaction color changed from red to light yellow at the end of the reaction. After stirring for 30 min at -78 °C the reaction was warmed to RT. Assay by 31P NMR showed the presence of phosphinidine (+249.5 ppm). TMSCl (0.2 mL) was added to quench TBSOLi, the solution was evaporated, and the residue was coevaporated with hexanes (10 mL). A solution of (cod)PdMeCl (0.265 g, 1.0 mmol) in CH2Cl2 (5 mL) was added to the crude phosphinidine and the mixture stirred at RT for 10 h. The color gradually changed from colorless to red-brown. After evaporation, the residue was dissolved in hexanes and purified on a 4 × 2.3 cm silica gel column, eluting first with hexanes (80 mL) to remove cod and ArPH2, then with CH2Cl2 (60 mL) to obtain the product. After evaporation the residue was triturated with hexanes (-30 °C) to give 0.63 g (87.1%) of 13 as yellow crystals. X-ray quality crystals were obtained by crystallization from acetonitrile at -30 °C. 1H NMR (CDCl3): 7.54 (d, 2H; J ) 3.4 Hz); 7.18 (d, J ) 18.9 Hz); 7.05 (s, 2H); 4.09 (septet, 2H; J ) 6.8 Hz); 2.86 (septet, 1H; J ) 6.9 Hz); 1.66 (s, 18H); 1.39 (d, 6H; J ) 6.8 Hz); 1.32 (s, 15H; accidental overlap of t-Bu and gem-dimethyl); 1.29 (d, 6H; J ) 6.8 Hz); 1.24 (Pd-Me; d, 3H; J ) 4.7 Hz); 1.23 (d, 6H; J ) 6.9 Hz). 13C{1H} (CDCl3) 173.3 (d, JC-P ) 55.3 Hz); 156.0 (d, JC-P ) 3.2 Hz); 154.1; 153.7 (d, JC-P ) 2.6 Hz); 152.0; 123.9 (d, JC-P ) 8.9 Hz); 123.6 (d, JC-P ) 8.7 Hz); 123.0; 122.5 (d, JC-P ) 2.5 Hz); 58.0 (d, JC-P ) 7.1 Hz); 39.4 (d, JC-P ) 1.3 Hz); 35.5; 34.4; 34.2 (d, JC-P ) 2.3 Hz); 32.6; 31.3; 29.9 (d, JC-P ) 16.0 Hz); 26.5; 24.0; 23.6; 10.8 (Pd-Me; d, JC-P ) 5.7 Hz). 31P{1H} NMR (C6D6): +219.1 ppm. Anal. Calcd for C38H62ClPPdS: C 63.05, H 8.63. Found: C 62.94, H 8.64. [(2,4,6-(i-Pr)3C6H2)SMe2CHdPMes*)Pd(NCMe)Me]+B(ArF)4-, 14. The synthesis was performed as in the case of 6a, using 13 (0.160 g, 0.22 mmol) and NaB(ArF)4 (0.200 g, 0.22 mmol). Product was obtained as a reddish foam, 0.320 g (91.3%). 1H NMR (CD2Cl2): 7.66 (d, 2H; J ) 4.2 Hz); 7.33 (d, 1H; J ) 18.5 Hz); 7.23 (s, 2H); 4.01 (septet, 2H; J ) 6.8 Hz); 2.96 (septet, 1H; J ) 6.9 Hz); 2.04 (s, 3H); 1.68 (d, 18H; J ) 0.8 Hz); 1.44 (d, 6H; J ) 2.2 Hz); 1.38 (d, 6H; J ) 6.8 Hz); 1.37 (s, 9H); 1.31 (d, 6H; J ) 6.8 Hz); 1.28 (d, 6H; J ) 6.9 Hz); 1.19 (Pd-Me; d, 3H; J ) 2.6 Hz). 31P{1H} NMR (CD2Cl2): +210.0 ppm (s). 13C{1H} (CD2Cl2): 176.9 (d, JC-P ) 62.9 Hz); 156.8 (d, JC-P ) 3.8 Hz); 156.0 (d, JC-P ) 3.1 Hz); 154.5; 154.3; 124.8 (d, JC-P ) 10.0 Hz); 124.2; 121.5 (d, JC-P ) 2.0 Hz); 121.0 (d, JC-P ) 20.3 Hz); 120.0; 60.1 (d, JC-P ) 3.3 Hz); 39.9 (d, JC-P ) 1.7 Hz); 36.0; 34.9; 34.5 (d, JC-P ) 1.7 Hz); 33.3; 31.2; 29.8 (d, JC-P ) 16.5 Hz); 26.6; 23.9; 23.6; 12.2 (Pd-Me; d, JC-P ) 5.6 Hz), 3.1. 31P{1H} NMR (CD2Cl2): +210.0 ppm. Anal. Calcd for C72H77BF24NPPdS: C 54.29, H 4.87, N 0.88. Found: C 54.52, H 4.92, N 0.85. (2,4,6-(i-Pr)3C6H2)SCMe2CHdN(2,6-(i-Pr)2C6H3), 16. To a solution of 2-methyl-2-(2,4,6-tri-isopropylphenylthio)propanal (0.556 g, 2.0 mmol) in methanol (4 mL) was added formic acid (4 drops) and 2,6-diisopropylaniline (0.76 mL, 4.0 mmol, Aldrich). The reaction was stirred for 20 h at RT. TLC assay showed that reaction was completed at that time. After

Phosphinidine-Palladium Complexes

Organometallics, Vol. 21, No. 26, 2002 5943

Table 4. Crystallographic Data Collection Parameters for 4a, 6a, 10a, and 13 4a formula mol wt cryst syst space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z dens calcd, Mg/m3 F(000) cryst dimens, mm temp, °C radiation (λ, Å) 2θ range, deg µ, mm-1 total no. of reflns total no. unique reflns no. of obsd data (I>2.5σ(I)) no. of refined params RF, % RW, % GOF

C39H54NP 567.83 monoclinic P21/n 15.2092(5) 9.6929(3) 24.5249(8)

6a

10a

3566.74(20) 4 1.057 1240.95 0.30 × 0.30 × 0.25

C74H72F24N2BPdP*1/3H2O 1599.53 triclinic P1 h 13.7601(8) 14.3900(8) 21.0682(12) 107.898(1) 100.978(1) 92.510(1) 3873.7(4) 2 1.371 1630.24 0.30 × 0.30 × 0.15

5.00-60.00 0.1 41835 6330 5169

5.00-50.00 0.36 31618 12659 5914

3969.82(23) 4 1.233 1558.08 0.25 × 0.20 × 0.10 -100 0.71073 5.00-60.00 0.65 56392 11600 8620

587 0.053 0.057 2.4486

933 0.068 0.075 2.345

389 0.044 0.054 1.9720

99.420(1)

evaporating solvent, the residue was purified by flash chromatography on silica gel (12 × 3.3 cm) in 1:1 hexane/toluene. Fractions containing the product were evaporated to give product as a yellowish oil (0.822 g, 88.3%). Rf ) 0.44 (1:2 toluene/hexane). 1H NMR (CDCl3): 7.74 (s, 1H); 7.34-7.10 (m, 3H); 7.09 (s, 2H); 4.09 (septet, 2H; J ) 6.9 Hz); 3.00 (septet, 2H; J ) 6.9 Hz); 2.94 (septet, 1H; J ) 6.9 Hz); 1.52 (s, 6H); 1.31 (d, 6H; J ) 6.9 Hz); 1.24 (unresolved br d, 12H); 1.22 (d, 12H; J ) 6.9 Hz). 13C{1H} (CDCl3, 238 K): 168.5, 154.8, 150.5, 147.8, 137.6, 124.8, 124.1, 122.9, 121.9, 52.2, 34.3, 32.3, 27.7, 25.9, 25.8, 24.1, 23.6, 22.9. Anal. Calcd for C31H47NS: C 79.93, H 10.17, N 3.01. Found: C 79.78, H 10.22, N 2.98. [(2,4,6-(i-Pr)3C6H2)SCMe2CHdN(2,6-(i-Pr)2C6H3)]PdMeCl, 17. Imine 16 (0.200 g, 0.43 mmol) was mixed with (cod)PdMeCl (0.114 g, 0.43 mmol) and benzonitrile (5 mL). The reaction mixture was stirred at RT for 1 h followed by evaporation of benzonitrile at 0.2 mm/RT overnight. The residue was coevaporated with toluene (2 × 5 mL), dissolved in CH2Cl2 (5 mL), and filtered through Celite. After evaporation and trituration with hexanes a yellowish solid was obtained (0.237 g, 88.5%), as a ca. 7:1 isomer mixture (ratio of Me peaks at 0.57 (major) and 0.79 ppm (minor)). The configuration at the palladium center was verified by X-ray crystallography; however, it was not possible to fully refine the structure due to twinning of the crystals. Major isomer 1H NMR (CDCl3): 7.55 (s, 1H); 7.25-7.08 (m, 5H); 4.38 (septet, 2H; J ) 6.8 Hz); 3.16 (septet, 2H; J ) 6.8 Hz); 2.93 (septet, 1H; J ) 6.9 Hz); 1.55 (s, 6H); 1.44 (d, 6H; J ) 6.8 Hz); 1.37 (d, 12H; J ) 6.8 Hz); 1.28 (d, 6H; J ) 6.9 Hz); 1.15 (d, 6H; J ) 6.8 Hz), 0.57 (s, 3H). Major isomer 13C{1H} (CDCl3): 175.4, 154.2, 153.2, 144.5, 139.4, 127.1, 123.7, 123.4, 119.8, 62.9, 34.4, 32.6, 28.3, 26.6, 25.7, 25.0, 24.0, 23.9, 23.5, -6.2. Anal. Calcd for C32H50ClNPdS: C 61.72, H 8.09, N 2.25. Found: C 61.86, H 8.12, N 2.31.

13

C38H61PdSClPN 736.78 monoclinic P21/c 13.1700(4) 26.5085(9) 11.5411(4)

C40H65SClPdPN 764.84 monoclinic P21/n 11.9591(5) 15.8500(7) 23.3435(10)

99.848(1)

104.795(1) 4278.1(3) 4 1.188 1622.11 0.20 × 0.20 × 0.20 5.00-50.00 0.61 36040 7572 6236 407 0.038 0.050 1.9215

[((2,4,6-(i-Pr)3C6H2)SCMe2CHdN(2,6-(i-Pr)2C6H3))Pd(NCMe)Me]+B(ArF)4-, 18. The synthesis was performed as in the case of 6a, using 17 (0.08 g, 0.128 mmol) and NaB(ArF)4 (0.114 g, 0.128 mmol). Product was obtained as a yellowish powder, 0.180 g (96.9%). The configuration at the palladium center was assigned by analogy with 17. 1H NMR (CD2Cl2): 7.71 (s, 1H); 7.34-7.25 (m, 3H); 7.24 (s, 2H); 4.18 (septet, 2H; J ) 6.8 Hz); 3.05 (septet, 2H; J ) 6.8 Hz); 2.96 (septet, 1H; J ) 6.9 Hz); 1.73 (s, 3H); 1.60 (s, 6H); 1.41 (d, 6H; J ) 6.8 Hz); 1.39 (d, 6H; J ) 6.8 Hz); 1.34 (d, 6H; J ) 6.8 Hz); 1.28 (d, 6H; J ) 6.9 Hz); 1.19 (d, 6H; J ) 6.8 Hz); 0.56 (s, 3H). 13C{1H} (CD2Cl2): 177.9; 155.3; 154.3; 143.3; 139.5; 128.6; 124.8; 124.5; 120.1; 67.5; 34.9; 33.5; 28.8; 26.5; 25.5; 25.1; 24.0; 23.8; 23.3; 2.1; -2.9. One aromatic carbon is unaccounted for. Anal. Calcd for C66H65BF24N2PdS: C 53.14, H 4.39, N 1.89. Found: C 53.42, H 4.43, N 1.82. X-ray Crystal Structures. Diffraction data were collected on a Bruker SMART diffractometer using the ω-scan mode. Refinement was carried out with the full-matrix least-squares method based on F (NCRVAX) with anisotropic thermal parameters for all non-hydrogen atoms. Hydrogen atoms were inserted in calculated positions and refined riding with the corresponding atom. Complete details of X-ray data collection are given below in Table 4. For 4a, I > 3.0σ(I).

Acknowledgment. We are grateful to DuPont for support of this research. Supporting Information Available: X-ray crystallography data for 4a, 6a, 10a, and 13 and graphs for the determination of rates of migratory insertion. This material is available free of charge via the Internet at http://pubs.acs.org. OM020631X